The invention relates to a bicycle transmission. The purpose of the bicycle transmission is to transmit power from the bicycle pedals to the bicycle wheels, achieving a variety of speeds and power ratios.
A standard bicycle has a drive wheel, linked to bicycle pedals by a chain and sprocket assembly. Over the years, bicyclists have found it desirable to vary the drive ratio to adjust to various riding conditions. Multi-speed bicycles were developed, having a series of gears alterable by the rider, to achieve different gear ratios for differing terrain.
Typical multi-speed bicycles involve a chain and sprocket gear changing system. In this system, the chain is lifted from its current gear and guided across a series of gears of different sizes by a derailleur. The chain eventually catches the desired gear, and power can be transmitted from the pedals to the rear wheel. This type of gear exchange system has several limitations.
First, the gear changing operation can be quite slow. Often, the chain does not catch the gear right away. In the interim, power cannot be transmitted to the rear wheel. This delay can be significant under some circumstances.
Second, the gear changing operation in unreliable. The chain sometimes gets caught in between the gears, and can sometimes fall off the gear group altogether. These circumstances can be dangerous when travelling at a high speed, and can be quite inconvenient at least.
Third, since the gearing changing system is typically external, at least in part, dirt is carried by the chain throughout the gearing system, requiring frequent maintenance and adjustment.
U.S. Pat. Nos. 4,666,172 to Hartman, and 4,823,641 to Kuhn et al., describe bicycle transmissions having planetary gearing arrangements.
U.S. Pat. No. 4,955,247 to Marshall, describes a bicycle transmission that is operable by a lever, rather than by a flexible cable.
While these units may be suitable for the particular purpose to which they address, or to general use, they would not be as suitable for the purpose of the present invention as hereafter described.